Further details about the proposed improvements to East Anglia’s main line have been emerging after chancellor George Osborne pledged investment in the route during the run-up to today’s Autumn Statement.

He said the government would “do what it takes” to get faster trains on the route – but there were few details about extra spending on the line. It came as part of an announcement of major transport infrastructure improvements in the region, including an A12 upgrade in Essex.

The Great Eastern Rail Taskforce has prepared a report saying an investment of £476 million in the line would be needed to allow trains to run between the capital and Norwich in 90 minutes, and between London and Ipswich in 60.

However there is no firm pledge to cover all that money – although £270m is already in the current Network Rail five-year plan for improvements which runs until 2019.

Transport secretary Patrick McLoughlin, who was at Liverpool Street Station to give his backing to the rail pledge yesterday, said: “I think all these issues about infrastructure do take time to be delivered. But in rail terms, the next five years I think would see quite of lot of what is being asked for in this report being delivered.”

He added: “What changes today is I am committing to the Government working along with the taskforce to deliver Norwich in 90.”

Rail and government insiders say this investment will allow track speeds to be increased, allowing some trains to achieve the Norwich in 90 goal.

However the extra £200 million will be needed before Network Rail can build new track in Essex and rebuild Haughley junction north of Stowmarket – which are both vital to build resilience into the network and allow trains to regularly travel at higher speeds.

Those works should be completed during Network Rail’s next five-year period, 2019-24. A government source said there was no point bringing the last £200m forward before that because the work could not begin until 2019 because of operational issues.

Another key issue is the Chancellor’s decision to allow the franchise-holder for the route after 2016 to pay less to the Treasury than Abellio Greater Anglia currently pays.

Officials say that means there will be no need for the successful bidder to run old, but cheap, trains – and running new modern trains by 2020 will be a key part of the franchise requirements.

Ipswich MP Ben Gummer, who has been a leading member of the Taskforce, said: “This is a very significant development for the region’s railways. I always said it will not happen overnight but the improvements are being mapped out.”

Abellio Greater Anglia managing director Jamie Burles said: “We are delighted that the government is backing the recommendations of the Great Eastern Rail Taskforce.

“We can now look forward to real enhancements to services on the GEML over the next decade.

“The positive momentum will start to really gather pace early in the New Year as our major refurbishment programme for the current intercity trains gets under way.”